The present invention relates to an electromotive adjustment device, in particular for use with adjustable flap valves.
An electromotive adjustment device of a type involved here finds application especially in heating, air-conditioning and ventilation systems for opening and closing a control element of a flap valve. The respective adjusting movement depends hereby on the intended purpose. For example, in case of fire, it may be necessary to open or close the flap valves, whereby it is demanded that the pivoting movement of the control element should not be assumed by the drive motor but by an energy storage member, such as a tensed spring, so as to ensure execution of the necessary movement, even when the drive motor fails to operate as a consequence of external impacts, e.g. elevated temperature. The energy storage member is hereby biased, when the control element is moved from a base position to the operative position that is normally assumed by the control element. There may, however, also be situations which require movement of the control element into different positions at short intervals in response to a change in temperature.
Swiss Pat. No. CH-A-614507 and U.S. Pat. No. 4,669,578 describe each an electromotive adjustment device with drive motors in the form of brush motors having a fixed external stator and a rotating armature to thereby drive the output journal. Mounted non-rotatably onto the output journal are spur gears to operate the drive train. Drive motors of this type generate sparks during startup, thereby progressively wearing off the drive motor. As the adjustment devices involved here are primarily intended for heating and ventilation systems, a precise control requires the motor to be started momentarily at relatively short intervals.
The partial circle or outer diameter of the gear wheels mounted onto the output journals is significantly greater than the diameter of the output journal. As a result, the number of teeth is correspondingly high so that the first gear stage to reduce the motor speed requires either the application of a gear wheel with correspondingly great number of teeth for engagement with the gear wheel on the output journal, or the rotation speed of this gear wheel has to be relatively high. In either approach, the housing of the adjustment device is of substantial size. Normally, in adjustment devices of the type involved here, the rotation speed of the output members of the drive train is extremely low. As the installation space is relatively small, the use of conventional adjustment devices caused problems that even render their installation prohibitive. In addition, conventional adjustment devices have to be suited to the rotation direction of the control element. In other words, counterclockwise rotation and clockwise rotation require an electric switchover.
It would therefore be desirable and advantageous to provide an improved electromotive adjustment device which obviates prior art shortcomings and which has small dimensions and does not require a switchover for moving the control element in both rotation directions, while yet being reliable in operation, even when the drive motor malfunctions.